How many days are in 3 weeks?

To determine how many days are in 3 weeks, it's essential to know the number of days in one week. There are 7 days in one week. Therefore, to find the total number of days in 3 weeks, you multiply the number of weeks by the number of days in a week:

3 weeks × 7 days/week = 21 days.

This calculation clearly shows that in 3 weeks, there are 21 days. This understanding of weeks and days directly supports the answer provided.